This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We observed that CheA[unreadable]289, which is composed of domains P3-P4-P5 of CheA weakly aggregates in solution. In the crystal structure, CheA[unreadable]289 molecules associate with each other via a hydrophobic interface at the end of sub-domain 2 of P5 domain. We use magnetic dilution experiments, disulphide cross-linking experiments and pulsed dipolar ESR to further investigate this binding interface.